Diamond has a number of properties which make it attractive for use in various applications. Among these properties are extreme hardness and excellent transmissivity of certain radiation. Diamond is also an extraordinary heat conductor, thermally stable, and an electrical insulator. However, natural diamond is prohibitively expensive for applications which require any substantial size and is difficult to form into certain shapes.
In recent years, a number of techniques have been developed for synthesizing diamond and for depositing synthetic diamond on surfaces of various shapes to obtain a diamond film or coating. These techniques include so-called high-pressure high-temperature ("HPHT") methods and chemical vapor deposition ("CVD") methods. The CVD methods include plasma deposition techniques wherein, for example, plasmas of a hydrocarbon and hydrogen are obtained using electrical arcing. The resultant plasma can be focused and accelerated toward a substrate using focusing and accelerating magnets. Reference can be made, for example, to U.S. Patent Application Serial No. 773,465, assigned to the same assignee as the present Application, for description of an example of a type of plasma jet deposition that can be utilized to deposit synthetic diamond on a substrate.
Synthetic diamond film can be deposited as a permanent coating on a substrate, such as on the wear surface of a tool or as an environmentally protective coating. Such films are generally considered to be relatively thin films. Alternatively, a synthetic diamond film that is generally considered a thick film, can be deposited on a substrate and then removed, preferably intact as a single "free standing" piece, for use in applications such as heat sinks, optical windows, and in tools. However, the obtainment of such thick films, especially of relatively large area, has proven troublesome. In addition to the difficulty of depositing quality synthetic diamond of substantial thickness, there is the problem of removing the diamond intact from the substrate. The substrate material will generally have a different coefficient of expansion than the diamond, as well as a different molecular and chemical structure. The adherence and growth of the diamond film, as well as its release, will depend, inter alia, on the materials used, surface preparation, and deposition parameters.
Titanium nitride and other materials have been used as a coating for a substrate, such as molybdenum, upon which synthetic diamond is to be deposited. Titanium nitride adheres reasonably well to molybdenum. Diamond can be deposited over a thin layer of the titanium nitride and then, ideally, released from the substrate after the desired thickness of synthetic diamond film has been deposited, such as by chemical vapor deposition. The diamond is deposited at a relatively high temperature and, as the diamond (as well as the titanium nitride interlayer and substrate below) cools after completion of the diamond deposition, the diamond should be released from the substrate, preferably in one piece. However, problems have been found to occur in the procedure. One of these problems is premature flaking off of the diamond and/or its underlayer during deposition or premature release of the diamond before deposition is complete. A further problem is cracking of the diamond upon its release from the substrate.
It is among the objects of the present invention to provide a solution to the indicated problems, and to generally improve the fabrication of free-standing synthetic diamond by chemical vapor deposition process.